v2v: -o glance: Fix metadata for disk type and NIC (RHBZ#1161575).

The labels 'hw_disk_bus' and 'hw_vif_model' were swapped.  This
happened to work for virtio guests.  For non-virtio guests you ended
up with absurdities like requiring an rtl8139 driver for the disk.

Thanks: Junquin Zhou